Exploring Novel Electronic Structures of Topological Quantum Matter

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Electronic materials play a tremendous role in almost every aspect of modern life - from supercomputers to household electronics - and the behavior of electrons in these materials determines their rich and unusual properties. Historically, the discoveries of novel electronic quantum materials have caused revolutions in our lifestyle and economy, such as the discovery of semiconductors. Very recently, an entirely new type of electronic materials, the topological insulator, was theoretically predicted and experimentally realized.Topological insulators represent a brand new state of quantum matter that is distinct to ALL previously known states. On the face of it, they are well-known, off the shelf materials; but they have profound, yet previously overlooked properties that make them so unique. In its pure form, a topological insulator has a full energy gap in the bulk electron band (thus like an insulator); while on the surface, it has metallic states formed by electrons with linear energy-momentum relationship (similar to photons that do not possess rest mass!) with their spin polarization completely determined by their moving directions. More dramatically, these unusual electrons are extremely robust, and can flow on the surface of topological insulators against any non-magnetic impurities, crystalline defects or surface distortions. Due to the great scientific significance and technological potential, topological insulators have grown as one of the most intensely studied fields in condensed matter physics within the last few years.However, while the scientists worldwide are advancing the frontier of this exciting field, there remain many challenges before we can actually realize the many amazing quantum phenomena (such as the magnetic monopoles, half electron charge and many topological magneto-electric effects resulted from the revised Maxwell equations in topological insulators) and practical applications (such as novel electronic, spintronic and thermoelectric applications) topological insulators promise. For examples, current topological insulators typically have excessive bulk carriers, thus prevent the bulk from being insulating (which will mask the subtle topological effects from the surface electrons); and the small bulk energy gap also prevent them from being used in high (room) temperature electronic devices. Thus we would like to solve these problems by carrying out this project to improve the quality of current topological insulators, and search for even better topological insulators with larger bulk energy gap and more stable in regular environments. We will also explore the pathways to use the unusual electronic and spin properties of topological insulators in practical applications, such as ultra-low power electronics, novel spintronic devices, optoelectronic applications, high efficiency thermoelectric applications and catalysis applications.Furthermore, the swift development of topological insulators has also inspired the study of other new topological states, such as quantum anomalous Hall insulators, topological semi-metals, topological crystalline insulators and topological superconductors, etc. These new topological states will unlock the door to even richer exotic quantum phenomena (such as quantized Hall conductance without externally applied magnetic field, and the exotic Majorana fermions that are their own anti-particles) and more unconventional applications (from ultra-low integrate circuit to future topological quantum computers) Thus we will also search for these novel phases of quantum matter in this project.